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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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TDA7336 датащи(PDF) 8 Page - STMicroelectronics |
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TDA7336 датащи(HTML) 8 Page - STMicroelectronics |
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8 / 20 page  AUDIO MUSIC SENSOR (See Figure 2) Aim of this section is to detect interprogram spaces present on a recorded tape. Both the blanks (interprogram spaces) and the programs minimum detectable durations can be easily set by means of 2 external and inde- pendent time constants. Also the minimum detectable input signal level can be externally adjusted, by a dedicated gain network. Main blocks are: Variable gain limiter amplifier Signal detector circuitry Logic blocks able to avoid unproper operations. Operations Description (refer to the simplified schematic of Figure 2). a)The two channels left and right mean signal coming from the preamp chain (AC coupled) are added (current) at the AMS input and pre- sented to the limiter amplifier. The limiter am- plifier gain is internally fixed to 40dB, and it could be reduced by the R8 external resistor. The AMSVth threshold is fixed at 1V. The fol- lowing signal detector comparator informs of the presence of music signal (High level out) and avoids the erroneous detection of very low signal (like noise) as real program. b)The system moves in blank detection mode everytime the supply is turned on or, with power supplied, the AMS On/Off pin (to be driven by an open collector output) is turned off (T1 open). Once this condition has hap- pened, the capacitor C15 charges, defining a minimum reset time, long enough to reset the Flip-Flops FF1 and FF2 and to descharge the program detector external C7 capacitor. The charging current at the AMS SW pin is about 10 µA. It follows that the reset time (C15 x Vpin7)/IC15 is given approximately by 0.122 x C15 ns where C15 is in µF. c)From now on where the sum input signal (left- right) amplified by the limiter exceeds the sig- nal detector threshold (3) the capacitor C7 is forced to charge. When the voltage across this capacitor reaches the comparator COMP1 threshold voltage Vth1 (approx. 2 Vbe) FF1 is set and FF2 is reset. (4) It follows that Q1 is turned on discharging the program de- tection capacitor (C7). d)Always when there is a recorded zone, Q1 is on; it becomes off only if a blank section is reached. When, with a time constant control- led by the R9,C9 network the voltage at space detection time pin reaches Vth2 thresh- old (comparator COMP2) a true blank section is detected and the FF2 is set. (The minimum charging time is approximately given by: 0.69 x C9x R9 [sec] In this condition Q2 is on, forcing the open col- lector AMS output to go low, informing the user that a true blank section has been de- tected. The state is then able to start from the above point c). Figures 3-4 show the signal behaviour. The device is able to prevent false interspace de- tection and the end of the tape. (see Fig. 4). Note: (3): minimum RMS input signal is given by: Vin = AMSVth ⋅ 1K + R8 101K + R8 ⋅ 0.6 where Vin is the mean of left and right channels:: Vin = Vright + Vleft 2 (4): the charging current at pin 8 is about 20 µA (half input signal) so program detection time constant is given by: C7 x 2Vbe 20 µA = 70 xC7 [µF] = [msec] It is recommended to insert a resistor (R7) high enough to prevent fast C7 capacitor discharging. TDA7336 8/20 |
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